ESE-1 (Elf3 in mouse), a novel ETS transcription factor, is expressed predominately in epithelial tissues in physiological conditions. In inflammatory disorders, ESE-1 is expressed in multiple cell types, including chondrocytes, in response to interleukin-1 (IL-1) and other proinflammatory cytokines. Our recent findings indicate that ESE-1 is a critical regulatory factor involved in cartilage loss during osteoarthritis (OA). We have shown that ESE-1 suppresses type II collagen gene (COL2A1) expression by binding to the COL2A1 promoter and by interacting with Sox9 and CBP. Our preliminary data show that ESE-1 also increases matrix metalloproteinase (MMP)-13, a key collagen-degrading enzyme in OA, by binding to ETS/PEA3 sites in the MMP13 promoter and cooperating with Runx2 and AP-1. The absence of MMP-13 protein in the Ese1/Elf3-deficient mouse, and the increased Ese1 expression in the articular cartilage of the cho/+ mouse model of OA compared to wild type mice, further suggests its pivotal role in cartilage degeneration during OA progression. Thus, we hypothesize that ESE-1 is a novel transcriptional regulator of cartilage destruction in OA. Specific Aim 1 is designed to: Identify the signaling pathways involved in ESE-1 induction and activation by inflammatory cytokines and in ESE1-mediated MMP-13 gene regulation. We will use chondrocyte culture models to characterize: (a) the signaling and transcriptional mechanisms involved in ESE-1 induction by different inflammatory stimuli;(b) the regulation of MMP-13 promoter activity via functional ETS-binding motifs responsive to ESE-1, as well as potential contributions of other ETS factors, Runx2 and AP-1;and (c) the structural features and phosphorylation sites that determine ESE-1 activity. Specific Aim 2 will: Determine whether Ese1/Elf3 deficiency protects against or attenuates cartilage loss in surgical and genetic mouse models of OA. We will use Ese1/Elf3-deficient mice to examine whether ablation of ESE- protects against cartilage damage induced by biomechanical challenge or by a genetically abnormal matrix in the Cho/+ mouse model that develops a spontaneous form of agedependent OA. In Specific Aim 3 we will: Determine the effects of ESE-1 overexpression on onset and progression of OA in mouse knee joints due to aging and surgical OA. We will generate Tet-off-inducible Ese1 transgenic mice to determine whether ESE-1 overexpression, by itself, initiates cartilage degeneration or accelerates surgically induced OA. Deciphering the mechanism of action of ESE-1 by these in vivo and in vitro approaches will enable us to identify novel therapeutic strategies to retard cartilage matrix degeneration during OA and aging. Project Description